Re: [PATCH] lower-bitint: Force some arrays corresponding to large/huge _BitInt SSA_NAMEs to BLKmode

[Richard Biener <rguenther@suse.de>]

On Thu, 18 Jan 2024, Jakub Jelinek wrote:

> Hi!
> 
> On aarch64 the backend decides to use non-BLKmode for some arrays
> like unsigned long[4] - OImode in that case, but the corresponding
> BITINT_TYPEs have BLKmode (like structures containing that many limb
> elements).  This both isn't a good idea (we really want such underlying vars
> to live in memory and access them there, rather than live in registers and
> access their parts in there) and causes ICEs during expansion
> (VIEW_CONVERT_EXPR from such OImode array to BLKmode BITINT_TYPE), so the
> following patch makes sure such arrays reflect the BLKmode of BITINT_TYPEs
> it is accessed with (if any).
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

So the issue is only manifesting during expansion?  I think it would
be better to detect the specific issue (V_C_E from register to BLKmode)
in discover_nonconstant_array_refs_r and force the register argument
to stack?

> 2024-01-18  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* gimple-lower-bitint.cc (gimple_lower_bitint): When creating
> 	array VAR_DECL for BITINT_TYPE SSA_NAMEs which have BLKmode, force
> 	DECL_MODE of those vars to be BLKmode as well.
> 
> --- gcc/gimple-lower-bitint.cc.jj	2024-01-17 14:43:33.498961304 +0100
> +++ gcc/gimple-lower-bitint.cc	2024-01-17 14:50:50.252889131 +0100
> @@ -6348,7 +6348,15 @@ gimple_lower_bitint (void)
>  	  tree s = ssa_name (i);
>  	  int p = var_to_partition (large_huge.m_map, s);
>  	  if (large_huge.m_vars[p] != NULL_TREE)
> -	    continue;
> +	    {
> +	      /* If BITINT_TYPE is BLKmode, make sure the underlying
> +		 variable is BLKmode as well.  */
> +	      if (TYPE_MODE (TREE_TYPE (s)) == BLKmode
> +		  && VAR_P (large_huge.m_vars[p])
> +		  && DECL_MODE (large_huge.m_vars[p]) != BLKmode)
> +		DECL_MODE (large_huge.m_vars[p]) = BLKmode;
> +	      continue;
> +	    }
>  	  if (atype == NULL_TREE
>  	      || !tree_int_cst_equal (TYPE_SIZE (atype),
>  				      TYPE_SIZE (TREE_TYPE (s))))
> @@ -6359,6 +6367,11 @@ gimple_lower_bitint (void)
>  	    }
>  	  large_huge.m_vars[p] = create_tmp_var (atype, "bitint");
>  	  mark_addressable (large_huge.m_vars[p]);
> +	  /* If BITINT_TYPE is BLKmode, make sure the underlying
> +	     variable is BLKmode as well.  */
> +	  if (TYPE_MODE (TREE_TYPE (s)) == BLKmode
> +	      && DECL_MODE (large_huge.m_vars[p]) != BLKmode)
> +	    DECL_MODE (large_huge.m_vars[p]) = BLKmode;
>  	}
>      }
>  
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)